Chemical polishing method



Feb. 14, 1961 c. c. 'COHN ETAL 2,971,826 CHEMICAL POLISHING METHOD FiledNov. 3, 1954 INVENTOR. CHARLES C. GOHN 8 SAMUEL L. GOHN fiwii m,

ATTORNEYS United States Patent OfiFice 2,971,826 Patented Feb. 14, restCHEMICAL POLISHING METHOD Charles C. Cohn, Atlantic City, NJ., andSamuel L. Cohn, Philadelphia, Pa., assignors to Samuel L. Colin andCharles C. COllH, copartners, trading as Colonial Alloys Company,Philadelphia, Pa.

Filed Nov. 3, 1954, Ser. No. 466,556 2 Claims. (Cl. 41-42) Thisinvention relates to article treating method and apparatus and hasparticular reference to the interruption of chemical actions on metals.

In the art of treating metals and metal alloys, as in etching,brightening, plating, electrochemical polishing, and the like, there areused treating baths whose compositions continue to react with the metalsurfaces being treated after withdrawal of the surfaces from thetreating bath. These continued reactions are often objectionable in thatthey impair the desired surface by etching it to too great an extent orotherwise changing the characteristics of the subsequent coating or ofthe basis metal. The evolution of noxious or dangeroues fumes or spraysalso makes these continued reactions undesirable.

For example, there may be considered the treatment of surfaces such asthose of aluminum or aluminum alloys which frequently involve thenecessity for treatment during only a limited time. The attainment ofthe desired action in some cases may be critical as to time, and then itis desirable at the expiration of such time to remove the article fromthe treating bath as rapidly as possible and subject it to rinsingusually by immersion in a rinsing bath or by washing the reactingmaterial from the article by a stream of rinsing liquid. When manualtransfer is used, the time involved between removal from the active bathand insertion into rinsing liquid may be small and relativelyinsignificant if the operator works rapidly. However, where an automaticoperation is involved with the articles being treated moved through thetreating bath on a conveyor, the conveyor speed is generally set by thetime of treatment required and the transfer from the treating bath to arinsing bath is necessarily slow unless mechanically complex devices areresorted to which, for example, transfer the articles from a slow movingconveyor to a rapidly moving one, or the like.

Furthermore, it is not practical to add the time of transfer to thetreating time in the bath on the supposition thatadhered liquid willcontinue to react properly, simply because the adhering liquid willgenerally channel on the metal surface, becoming irregularlydistributed, and with certain portions becoming exhausted more rapidlythan others, resulting in non-uniform action. Furthermore, inmany'instances, the conditions of such further action change. Forexample, some actions give proper results only at high temperatures andat lower temperatures produce undesired results. In this connectionthere may be cited the chemical brightening of aluminum and its alloysthrough the use of mixtures of phosphoric and nitric acids as describedin the application of Charles C. Cohn, Serial No. 404,436, filed January18, 1954, now US. Patent No. 2,729,551. For bright specular finishes ofthe most desired types, the action, which is a rapid one, desirablytakes place at quite high temperatures in the region of or exceeding 100C. As the temperature of the treatment drops, the action tends more andmore to become one of production of diffuse and then matte surfaces, andthe latter only are produced at or around room temperatures.Accordingly, if aluminum articles are thus being treated and are removedfrom the bath operating at proper temperature, if the solution is notvery promptly removed and is permitted to continue action while thearticle is suspended in the air and while the temperature substantiallydrops, the continued action may destroy the specular surface produced inthe bath and result in the formation of an unsatisfactory matte surface.

Furthermore, exposure to the atmosphere in many cases plays a part.While in the treating bath, the limited exposed surface of the bath andthe bath composition itself may effect practical isolation from theoxygen in the atmosphere; whereas if the article is Withdrawn from thebath and is undergoing draining therefrom of the bath liquid, theexposure to atmospheric oxygen may rapidly discolor or otherwiseadversely affect the surface finish.

It is the general object of the present invention, therefore, to providea method and apparatus for the treatment of metallic surfaces whereby adesired treating reaction may be abruptly discontinued particularlyunder conditions, for example, of automatic conveyor operation, where itis impractical or costly to secure a rapid transition from the treatingbath to a rinse or quenching bath. However, the invention is not limitedto automatic conveyor operation, but is applicable to manual operationswherein it permits more leisurely manipulation of the work, preventsspoilage in the event that through some mismanipulation the handling ofthe Work is abnormally slowed down, and serves to protect the operatoragainst noxious or dangerous fumes. In accordance with the invention,the articles immediately upon removal from the active bath, eitherautomatically or manually, are subjected to an atmosphere which promptlyinhibits further action of detrimental type while permitting thearticles to move relatively slowly in the transition stage between thetreating bath and a rinsing or quenching bath. Usually, the last type ofbath is desirably used though, in some cases, it may be omitted. Inaccordance with the invention, furthermore, there is only negligibleintroduction into the treating bath of materials which will dilute thebath or add deleterious substances which would shorten its effectivelife. The objects of the invention relate to the attainment of resultsof the type indicated, and these broader objects together with detailedobjects will become apparent from the following description read inconjunction with the accompanying drawing in which:

Figure 1 represents diagrammatically a typical type of apparatus whichmay be utilized for carrying out the invention; and

Figure 2 represents diagrammatically an apparatus wherein the inventionis applied to manual Work handling.

The apparatus will be first described without specific reference to thechemical aspects of what is involved.

The treating tank 2 contains the bath B in which the articles to betreated are immersed. The articles are conventionalized at A and aresupported by the conveyor chains 4, two such chains generally beingprovided with cross members 5 by which the articles A are supported. Thearticles represented by A may be quite general:

ported by hooks or otherwise from the members 5, or

" A may be taken to represent racks of suitable metal on which thearticles are supported in any suitable fashion. The articles to whichthe invention relates are those presenting metallic surfaces to betreated, and may or may not be completely metallic. They may, in fact,comprise several metals of which only one is to undergo treatment, andin such case areas or metals which are not to be treated may be coatedwith suitable resists.

The conveyor carrying the articles A is guided over and under sprockets6 and 8 to provide immersion of the articles in the bath B. it may beassumed that a substantial time of immersion in the bath is required,and if the length of the tank 2 is of reasonable extent, this willgenerally mean that the conveyor may advance only at a relatively lowspeed. The conveyor 4 is caused to take a path to lift the articles outof thetank by being trained about the sprockets ill and 12, and it willbe evident that the removal of the article in itself necessarilyrequires a considerable time in proportion to the time of passagethrough the tank unless the bath is quite shallow in a relatively longtank.

What has been so far described would be typical of conveyor operation.In the absence of special provisions provided by the invention, thearticles would have to be subjected to a substantial time intervalbetween removal from the bath tank 2 and insertion in a rinse orquenching bath. During such interval, draining would take place with theproduction of irregularity of coating, exposure to air, possible partialdrying, local exhaustion of the active solution, change of temperature,or the like,

previously described as detrimental in the great majority of processes.An attempt to wash off the bath solution by a stream or spray of rinsingor quenching liquid would obviously, unless the application thereof wasdelayed, result in entry of the rinsing or quenching solution into thebath which would either rapidly dilute the bath or render it inoperativeby neutralization of its active ingredients.

in accordance with the present invention there is provided at thedischarge end of the tank 2 an enclosure 14 into and through'which thearticles are progressed during the passage of the conveyor chains aboutthe sprockets indicated at 16, 12, i6 and 18. This enclosure 14 isclosed to the maximum extent possible consistent with the entry and exitof the conveyor and the articles carried thereby. As shown, it hasbottom openings which overlap the discharge end of the tank 2 and thereceiving end of a tank 29 which contains the rinsing medium R. Tocomplete the picture of the path of the conveyor and the articles,reference may be made to the sprockets 22 and 24 which in conjunctionwith sprockets 18 serve to provide for progress of the articles throughthe rinsing bath and removal therefrom.

In accordance with the present invention there are provided, in itspreferred form, nozzles 26 which discharge a rinsing or quenching mediuminto the enclosure 14, the medium being provided through the manifold2%.

These nozzles are preferably of the well-known fog type producing adispersion of very fine droplets of the rinsing or quenching liquid. Asis known, such nozzles will produce a fog of a slowly settling type, dueto the very small size of the droplets, but at the same time provides ahigh concentration of the rinsing or quenching liquid per unit volume ofthe fog. There is thus provided an atmosphere through which the articlespass in their progress into, through, and out of the enclosure 14. Toprevent the entry of any substantial amount of the rinsing or quenchingliquid into the bath B, the enclosure 14 is provided with an exhaustpipe 36 through which flow is induced by a pump 32. By suitable locationand direction of the fog nozzles 26 relative to the entrance to theenclosure 14 and the path taken by the articles, and by the propercontrol of the removal of the atmosphere within the enclosure 14 by thepump 32, the air drawn into the enclosure at the entrance and exitopenings will serve to act as a barrier preventing settling of the fogparticles into the bath B and also into the rinsing or quenching bath R,though settlement of the fog particles into the latter may not beobjectionable. It will be evident to those skilled in the art that thelocation of the fog within the enclosure 14 may be readily controlled tosecure 'a proper location thereof as may be observed, for example, byproviding transparent windows in the enclosure to enable properadjustments to be made. If the fog is of the desirable nonsettling type,a considerable proportion of the fog will be withdrawn through theexhaust passage 30 which is desirably provided with a sump 34 for thecollection of the fog liquid which may settle out, and desirably theremaining portion of the fog passing the pump 32 is caused to settle outin a settling chamber 38 provided with baffles, with the result thatsubstantially only air will emerge from the exhaust passage 42. Theliquid collecting in the sump 34 and in the chamber 33 may be drawn ofithrough the respective pipes as and 43 and, in general, will besuitable'for reuse, being returned to the manifold 28. This is possiblesince that tog which emerges through exhaust passage 3% will, ingeneral, not

have been affected by the liquid carried by the articles out of the bathB.

Between the bath B and the rinse or quench bath R there is desirablyprovided a catcher 21 for liquid which drains from the articles. Thisliquid will comprise to a considerable extent liquid carried from thebath by the articles undergoing treatment and, in addition, will containthe fog liquid which has settled out on the article and has admixed withthe bath liquid to stop its action. Generally, therefore, the liquidwhich separates out at 21 is not suitable either for direct return tothe bath B or for recirculation to the manifold 23, but may be drawn offthrough the pipe 23 for the possible recovery of any constituents ofvalue which it may contain. It may be remarked, however, as will shortlyappear, that the liquid provided to the fog nozzles may be merely wateror a mixture of water containing one or more of the bath constituents,in which case the liquid leaving at 23 may possibly be concentrated togive a liquid which essentially has the composition or partialcomposition of the bath B and may be returned thereto or has acomposition constituting a suitable makeup or partial makeup for thebath B. 7

Considering the various aspects which the invention may take, thesimplest operation, and one which is a possibility in various instances,involves merely the introduction into the enclosure 14 of air which hasbeen cooled or quite substantially refrigerated, in which case fognozzles are, of course, unnecessary and may be replaced by such nozzlesas will merely produce an air blast. This type of operation may be usedwhen the action of the bath B takes place at elevated temperatures andthe activity of the bath which might be detrimental may be caused to berendered substantially ineffective merely by cooling. The passage of thearticles through the normal ambient atmosphere at room temperature inmany cases will not suifice to produce sufi'lciently rapid cooling toterminate the action of the bath, and in such cases refrigerated airwill lower the temperature of the article and the carried out bathliquid to such a. point that detrimental action will cease;

In other cases, and constituting the next simplest situation, the actionof the bath may be terminated merely by substantial dilution with waterof the bath solution which may be carried out by the articles. In suchcase, water may be admitted through the manifold 28 and dispersed in thefog nozzles 26. By the arrangement which is shown, this water,transformed into a fog the location of which may be controlled as setforth above, will not pass down into the bath B so as to dilute it andrender it ineffective. If water is so used, the dilute bath liquid willdrip from the articles as they pass over the catcher 21, and the dilutedsolution will be collected and rejuvenated by evaporation. In such acase, the rinsing or quenching bath would probably also consist merelyof water or possibly of some dilute solution of an acid or alkali and noparticular care need then be exercised to prevent water from the fogfrom entering this bath.

If water is used as just described, it may, of course, be cooled toprovide such low temperature as may in aim many cases serve to aid interminating the reaction'of the bath on the surfaces being treated inaddition to the results from dilution.

More usually, however, there is required for the rapid termination ofthe bath reaction the treatment of the wet metallic surface with someinhibiting chemical in solution. Such an inhibiting chemical willsometimes be quite detrimental to the treating bath B, and consequentlythe matter of preventing'its entrance into the bath B is of majorimportance. The invention attains particular value in a case such asthis, since the inhibiting solution may be fed to the fog nozzles 26 toproduce a fog which is effectively isolated from the bath B by thecontrol of its placement as described. In such case, the inhibitingreagent will generally act chemically upon the adhering liquid either toneutralize it or, at least, to neutralize its activity, possibly byrendering the metal surface inert to further bath action. The result isthat the liquid dripping from the articles after they enter the fog willnot be suitable for simple reclaiming for return to the bath B. Theliquid collected in 21, therefore, may either pass to waste, or may bechemically treated for recovery of any valuable constituents therein. Insome cases, of course, it may be used as a part makeup for theinhibiting liquid entering the manifold 28, though, in general, acertain amount will have to be removed to prevent undue concentration ofthe bath constituents.

In such cases, the rinsing or quenching bath R may or may not bedetrimentally affected by the fog liquid, and depending upon theparticular circumstances there may or may not be necessary precautionsto prevent the fog liquid from entering this rinsing or quenching bath.In many cases, the rinsing or quenching bath R may have the samecomposition as what is introduced through the nozzles 26, in which caseit would be immaterial whether the fog does or does not pass into thebath R. In fact, it may happen in certain instances that a suitablerinsing or quenching bath R may have the same active constituents as theliquid desirably entering into manifold 28, in which case the fog may becollected in the bath R or what is collected, as in the sump 34 andcollector'38 may be returned directly to the bath and may, in fact,constitute the makeup material forvthis bath.

In other instances, however, the inhibiting chemical may be aconstituent of the bath B. For example, consider the brightening ofaluminum as carried out by the treatment of aluminum or its alloys asdescribed in the application of Charles C. Cohn referred to above athigh temperatures by a mixture of phosphoric and nitric acids. Asalready pointed out, if this mixture is allowed to act at lowertemperatures an etching action will occur which will destroy the brightsurfaces produced at high temperatures. However, nitric acid added withor without water dilution at the lower temperatures will inhibit theetching action which is'due to the phosphoric acid. (The low percentageof nitric acid originally in the hot bath is not of sufficientconcentration to inhibit the phosphoric acid action in the cold.)Accordingly. in this case, cold nitric acid, either concentrated ordilute, may constitute the liquid fed to the nozzle 26 to provide thefog and will efiectively inhibit the undesired reaction which wouldotherwise continue. For example, the inhibiting composition may consistof 15% by weight of 70% HNO and 85% of water, though this solution mayvary greatly in composition. But in this case the inhibiting agent, thenitric acid, is a desirable constituent of the treating bath B as wellas of the rinsing bath R, and, consequently, the drained material at 23and the recovered fog at 36 and tion, if desired) for makeup of thisbath, or the recovered fog may be returned to rinse R from which, infact, there may be drawn the liquid to supply the nozzles. Inparticular, in this fashion the relatively costly H PO carried out ofthe treating bath may be recovered and used as makeup for the treatingbath, suitable amounts of H PO and/or nitric acid and/or water beingadded to secure a suitable makeup liquid. Thus, various 'cycles of thecomponents may be provided, depending upon the concentrations which itis desired to maintain.

Conversely, in the brightening of copper, nickel or the like by the useof hot phosphoric-nitric acid mixtures, it is the nitric acid which, atlower temperatures, has an undesirable etching effect while phosphoricacid acts as an inhibitor. In such case the matters discussed in thelast paragraph would be applicable but with an interchange of the nitricand phosphoric acids; i.e., dilute phosphoric acid would be thefog-forming inhibitor and also, if desired, the constituent of therinsing bath.

It will now be evident that the invention is of very broad applicabilityand is obviously not limited to any particular treatments, classes oftreatments, materials used, or classes of materials used. Examples,however, will be informative, though they are not be regarded assuggesting limitations on the method or apparatus.

Considering, for example, a bath B which may be strongly acid, or evenmoderately acid, the action of such a bath will usually be terminated byan increase in pH. In such a case, there is, of course, indicated theintroduction through the nozzle 26 of an alkaline solution which willraise the pH to such value as will stop the action.

Conversely, if the bath B is alkaline, its action may be terminated by.introducing an acidic solution to form the fog. In this connection, theterm acid is used quite broadly, since, for example, if the bath Bcontained as its active or energizing constituent a caustic alkali, andwould be rendered completely or substantially inactive if the alkalinitywas that of an alkali carbonate, it will be evident that the reactionmight well be terminated by the introduction of a bicarbonate solution.

Again there may be introduced a solution of a material which has whatmight be considered an inhibiting action as described above.

It will be evident that the invention is quite broadly applicable to thetreatment of numerous metals. Besides the brightening of aluminum asdescribed in my application referred to above through the use of hotmixtures containing phosphoric acid and nitric acid, with or with outsulfuric acid, the invention is applicable to the following procedureswhich are merely typical of a great number which may be used:

The treatment of aluminum with hot caustic soda for etching of itssurface is common and in this case the action may be inhibited byproviding an artificial atmos phere which may consist solely of coldair, may consist of a fog of water, or may consist of a fog of an acidmaterial capable of neutralizing the caustic soda to an extent stoppingits action on the aluminum. For this purpose, there may be used asolution such as that of sodium bicarbonate or other weakly acidicmaterial.

Alternatively, the fog may consist of a solution contain-- ing an alkalichromate or chromic acid which will have an inhibiting effect on theaction of the caustic soda.

In the case of treatment of magnesium or zinc with nitric or sulfuricacid, the atmosphere may be provided in the form of a fog of water or afog of an aqueous soIution of an alkali capable of neutralizing theacid.

In the treatment of copper, brass, nickel, German silver, or the like,with mixtures of phosphoric and nitric acids, with or without aceticacid or other materials, the inhibiting atmosphere may be provided by awater fog or by the fog of a solution of an alkali or phosphoric acid asdescribed above which will inhibit the action of the nitric acid, themajor active constituent of the bath.

Aluminum or its alloys may also be brightened using hydrofluoric acidwith or without nitric acid. The inhibiting atmosphere in such case maytake the form of a water fog or a fog of an alkali capable ofneutralizing the acid or acids or the fog of a chromate solution whichwill inhibit the action of the bath material.

Numerous other treatments in accordance with the invention will beevident to those skilled in the art.

Aside from inhibiting the action of the dragged-out bath solutions orcompositions, the invention has the further important aspect ofgettingrid of the hazards of noxious or dangerous fumes which areproduced in many treating processes and, in particular, surround thematerials as they are withdrawn from the bath. The artificial atmosphereproducing arrangement not only draws ofi such vapors but, in the case ofthe production of fogs, the material constituting the fog will dilute orreact with the fumesubstances to produce safe working conditions. A

Reference may now be made to Figure 2 which shows the modification of aconventional type of treating tank assembly for the manual handling(usually, by the use of crane-providing devices) of materials treated ina bath. In this figure, 44 represents the usual tank containing thetreating bath, and it may be. assumed that the operator stands to therigt of this bath to handle the materials undergoing treatment. It iscustomary in the case of a bath which gives rise to fumes to surroundthe upper edge of the tank with a trough-like venting system connectedto a suction fan to exhaust the fumes generated at the surface ofthebath. Additionally, above the tank, there is provided a hood ventconnected to an exhaust fan for the removal of fumes which rise from thematerial as it is lifted from the tank. In accordance with the presentinvention there is produced an atmosphere above the bath and below thehood 48 which is of the type previously discussed and into which thematerials undergoing treatment are raised as they emerge from the bath.Headers 52 and 56 running along the edges of the tank are provided withnozzles 50 and 54 which, depending upon the treatment involved, mayeither produce merely a cold atmosphere of air'or a fog of water or of aneutralizing or inhibiting solution as has been previously described. Inview of the exhaust conditions provided at 46 and by reason of the hood48, this fog is maintained directly above the tank and is drawn, inparticular, upwardly into the hood and may be separated as in themodification shown in Figure 1 by apparatus arranged in the exhaustconduit. By reason of this arrangement, not only is the action of thebath liquid arrested in the fashions already described but noxious ordangerous fumes are diluted or neutralized, or merely diminished byvirtue of cooling action, so as not to spread into the regions about thetank whereat they might reach and be dangerous to the operator. With thearrangement of, nozzles as indicated, the arresting action beginsalmostas soon as an arti le or a portion thereof is raised from the surface ofthe bath. With an exhaust system provided as illustrated, the amount offine fog material which will enterthe' bath will usually be negligibleso that the fog may be produced by a solution of a material which insubsantial quantities might be deleterious to the bath.

It will be evident that the invention may be carried out in otherfashions without departing from the principles of the invention asdefined in the. following claims.

What is claimed is: a

1. A method comprising the steps of immersing 'an article of aluminum oran alloy of aluminum in a bath comprising phosphoric acid, nitric acidand water having a brightening action on the surface of said article,-withdrawing said article from said bath at substantially. the time ofcompletion of the desired extent of said chemical action, and treatingsaid article immediately and while it carries adhering liquid from thebath with an aqueous solution of nitric acid adapted to stop furtherchemical action on the surface of the article. a

2. A method comprising the steps of immersing an article of aluminum oran alloy of aluminum in a bath comprising phosphoric acid, nitric acidand water having a brightening action on the surface of said article,with drawing said article from said bath at substantially the. time ofcompletion of the desired extent of said chemical action, treating saidarticle immediately and while it carries adhering liquid from the bathwith an aqueous solution of nitric acid adapted to stop further chemicalaction on the surface of the article, and thereafter using the lastmentioned treating solution as a makeup con stituent of the firstmentioned bath.

References Cited in the file of this patent UNITED STATES PATENTS1,908,487 Powers May 9, 1933 2,086,993 Barrett July 13, 1937 2,172,171Meyer Sept. 5, 1939 2,437,528 Hodil Mar. 9, .1948 2,541,901 Zademach eta1 Feb. 13, 1951 2,593,447 Hesch Apr. 22, 1952 2,632,693 Jenkins Mar.24, 1953 2,650,157 Cochran Aug. 25, 1953 2,689,785 Simon Sept. 21, 19542,699,382 Altenpohl Jan. 11, 1955

1. A METHOD COMPRISING THE STEPS OF IMMERSING AN ARTICLE OF ALUMINUM ORAN ALLOY OF ALUMINUM IN A BATH COMPRISING PHOSPHORIC ACID, NITRIC ACIDAND WATER HAVING A BRIGHTENING ACTION ON THE SURFACE OF SAID ARTICLE,WITHDRAWING SAID ARTICLE FROM SAID BATH AT SUBSTANTIALLY THE TIME OFCOMPLETION OF THE DESIRED EXTENT OF SAID CHEMICAL ACTION, AND TREATINGSAID ARTICLE IMMEDIATELY AND WHILE IT CARRIES ADHERING LIQUID FROM THEBATH WITH AN AQUEOUS SOLUTION OF NITRIC ACID ADAPTED TO STOP FURTHERCHEMICAL ACTION ON THE SURFACE OF THE ARTICLE.
 2. A METHOD COMPRISINGTHE STEPS OF IMMERSING AN ARTICLE OF ALUMINUM OR AN ALLOY OF ALUMINUM INA BATH COMPRISING PHOSPHORIC ACID, NITRIC ACID AND WATER HAVING ABRIGHTENING ACTION THE SURFACE OF SAID ARTICLE, WITHDRAWING SAID ARTICLEFROM SAID BATH AT SUBSTANTIALLY THE TIME OF COMPLETION OF THE DESIREDEXTENT OF SAID CHEMICAL ACTION, TREATING SAID ARTICLE IMMEDIATELY ANDWHILE IT CARRIES ADHERING LIQUID FROM THE BATH WITH AN AQUEOUS SOLUTIONOF NITRIC ACID ADAPTED TO STOP FURTHER CHEMICAL ACTION ON THE SURFACE OFTHE ARTICLE, AND THEREAFTER USING THE LAST MENTIONED TREATING SOLUTIONAS A MAKEUP CONSTITUENT OF THE FIRST MENTIONED BATH.